Optical detection of fluorescent liquid from a wood fibre web

Abstract

The invention relates to a method, comprising illuminating an area of a wood fibre web by directing ultraviolet light to an area of the web by an ultraviolet light source, capturing an image of at least part of the illuminated area by an imaging device comprising a colour filter, transmitting image data of the captured image to an image data processing device, and analysing if the captured image comprises a fluorescent liquid stain emitting fluorescent light passed through the colour filter. The invention further relates to a machine vision system and a computer program product for detecting fluorescent liquid stains from a wood fibre web.

The invention claimed is: 
     
       1. A camera detection method for detecting a wood fibre web, the method comprising:
 illuminating an area of the wood fibre web by directing ultraviolet light to an area of the web by an ultraviolet light source; capturing a first image of at least part of the ultraviolet illuminated area by an imaging device comprising a colour sensor, which is configured to filter reflected UV light from images illuminated by the ultraviolet light source; transmitting image data of the first image to an image data processing device; analysing if the first image comprises a fluorescent defect emitting fluorescent light passed through the colour sensor; wherein the method further comprises: illuminating the same area of the wood fibre web by directing non-ultraviolet light to the area of the web by a non-ultraviolet light source after capturing the first image; capturing a second image of at least part of the area illuminated with the non-ultraviolet illumination by the same imaging device; transmitting image data of the second image to the image data processing device; and analysing if the second image comprises a non-fluorescent defect, wherein the image data processing device is configured to find fluorescent defects from images illuminated by an ultraviolet light source and to find non-fluorescent defects from images illuminated by a nonultraviolet light source. 
 
     
     
       2. The method according to  claim 1 , wherein every other captured image is illuminated with the ultraviolet light and every other with the non-ultraviolet light. 
     
     
       3. The method according to  claim 1 , wherein a part of the captured images is illuminated with the ultraviolet light and the other part with the non-ultraviolet light. 
     
     
       4. The method according to  claim 1 , wherein the wood fibre web is a paper or cardboard web. 
     
     
       5. The method according to  claim 1 , wherein the colour sensor is a part of the imaging device or an imaging sensor of the imaging device. 
     
     
       6. The method according to  claim 1 , wherein the colour sensor is a green filter passing through wavelengths approximately 520-550 nm or a red filter passing through wavelengths approximately 640-730 nm, and wherein the fluorescent light emitted by the fluorescent liquid corresponds to wavelengths passed through the colour sensor. 
     
     
       7. The method according to  claim 1 , wherein the fluorescent liquid is produced by adding a fluorescent marker into liquid, or wherein the fluorescent liquid is inherently fluorescent. 
     
     
       8. The method according to  claim 1 , wherein the method further comprises increasing the intensity level of the captured image. 
     
     
       9. The method according to  claim 1 , wherein the non-fluorescent defects are holes, spots, streaks or wrinkles. 
     
     
       10. The method according to  claim 1 , wherein the method further comprises simultaneous detecting an edge of the web. 
     
     
       11. A camera detection machine vision system for detecting a wood fibre web wherein, the machine vision system comprises
 an image data processing device, which is configured to find fluorescent defects from images illuminated by an ultraviolet light source and to find non-fluorescent defects from images illuminated by a non-ultraviolet light source, an imaging device comprising a colour sensor, which is configured to filter reflected UV light from images illuminated by the ultraviolet light source, and an ultraviolet light source, which is configured to direct ultraviolet light to an area of the web, wherein the imaging device is configured to capture a first image of the ultraviolet illuminated area with the colour sensor and to transmit image data of the first image to the image data processing device for analysing if the first image comprises a fluorescent liquid defect emitting fluorescent light at wavelength spectrum passing through the colour sensor, wherein the machine vision system further comprises a non-ultraviolet light source that is after capturing the first image configured to direct non-ultraviolet light to the same area of the wood fibre web than the ultraviolet light source, and that the imaging device is further configured to capture a second image of at least part of the area illuminated with the non-ultraviolet illumination by the same imaging device, and to transmit the image data of the second image to the image data processing device for analysing if the second image comprises a non-fluorescent defect. 
 
     
     
       12. The machine vision system according to  claim 11 , wherein every other captured image is illuminated with ultraviolet light and every other with non-ultraviolet light. 
     
     
       13. The machine vision system according to  claim 11 , wherein a part of the captured images is illuminated with ultraviolet light and the other part with nonultraviolet light. 
     
     
       14. The machine vision system according to  claim 11 , or wherein the colour sensor is a part of the imaging device or an imaging sensor of the imaging device. 
     
     
       15. The machine vision system according to  claim 11 , wherein the colour sensor acts as a green filter passing through wavelengths approximately 520-550 nm or a red filter passing through wavelengths approximately 640-730 nm, and wherein the fluorescent light emitted by the fluorescent liquid corresponds to wavelengths passed through the colour sensor, and wherein the fluorescent light emitted by the fluorescent liquid corresponds to wavelengths. 
     
     
       16. The machine vision system according to  claim 11 , wherein the fluorescent liquid is produced by adding a fluorescent marker into liquid or wherein the fluorescent liquid is inherently fluorescent. 
     
     
       17. The machine vision system according to  claim 11 , wherein the non-fluorescent defects are holes, spots, streaks or wrinkles. 
     
     
       18. The machine vision system according to  claim 11 , wherein the non-ultraviolet light source is a LED. 
     
     
       19. At least one memory storing instructions to execute the method of  claim 1 . 
     
     
       20. The method according to  claim 1 , wherein the configuration of the image data processing device to find fluorescent or non-fluorescent defects comprises adjusting of intensity level of captured images. 
     
     
       21. The machine vision system according to  claim 11 , wherein the configuration of the image data processing device to find fluorescent or non-fluorescent defects comprises adjusting of intensity level of captured images.